Although traditional Chinese medicine advocates the use of acupuncture not only to induce analgesia but also to treat essential hypertension, acupuncture s postulated antihypertensive efficacy in humans has not been subjected to rigorous Western scientific testing. Before advocating acupuncture as an effective complimentary/alternative medicine strategy for essential hypertension, it is necessary to demonstrate that the beneficial effects of acupuncture are scientifically robust, long-lasting, and explicable in terms of modern scientific mechanisms. In spontaneously hypertensive rats, acupuncture-like electrical stimulation of thinly myelinated (Group III) somatic afferents activates central endorphin (naloxone-sensitive) pathways that elicit long-lasting decreases in sympathetic nerve activity (SNA) and blood pressure. The ability to record SNA with microelectrodes in conscious humans provides a new opportunity to test this novel mechanistic hypothesis in patients undergoing electroacupuncture, a modification of the ancient technique which provides a quantifiable and reproducible stimulus to human skeletal muscle afferents. Using a randomized, double- blind placebo-controlled design, we will test two major hypotheses: (1) Electroacupuncture produces a long-lasting reduction in SNA, thereby providing a safe and effective complimentary treatment of human hypertension. (2) A major mechanism mediating the blood pressure-lowering effect of acupuncture is the activation of somatic afferents which trigger a naloxone-sensitive reflex suppression of central sympathetic outflow. The distinctive features of this proposal are the use of quantitative, state-of-the-art techniques (e.g., microelectrode recordings of SNA, 24 hour ambulatory blood pressure monitoring) and a rigorous, tightly controlled experimental design to test novel mechanistic hypotheses regarding the effects of acupuncture on blood pressure in humans. Given the enormous interest in acupuncture by our lay public but the paucity of Western scientific data about its efficacy in cardiovascular disorders, our studies in normotensive and hypertensive humans should provide a conceptual framework for deciding whether to accept or reject the large body of Chinese (and Russian) literature advocating acupuncture as a safe and effective treatment of essential hypertension and other cardiovascular disorders (such as heart failure, and myocardial ischemia) in which there is an important sympathetic neural component.